As a result of their large physical height, wind turbines are often affected by lightning strikes. Most frequently, the lightning strikes in the region of the rotor blade tip when the rotor blade is pointing upwards at an angle or straight. In order to prevent destruction of the rotor blade by the lightning strike, it has long been known to arrange a lightning receptor in the region of the rotor blade tip and to connect it to a lightning conductor. The current from lightning striking the lightning receptor is then discharged via the lightning conductor to the rotor blade root, from there into the hub via the nacelle and the tower to ground. Primarily copper cables with a relatively large cross section are arranged within the rotor blade, in particular along a spar or shear web of the rotor blade, as lightning conductor.
In order to counteract icing-over of the rotor blades, electrical heating devices are used. These are made of an electrically conductive material and a heating current flows through them during operation; the heating current results in heating of the heating device. Such heating devices are additional electrically conductive structures in or on the rotor blade which are typically arranged over a large length more or less parallel to the lightning conductor. In the event of a lightning strike, electrical currents with very high and rapidly rising current intensities are discharged via the lightning conductor which, on the basis of Ampere's Law with Maxwell's correction, produces a severely variable magnetic field in the surrounding environment of the lightning conductor. On the basis of the Maxwell-Faraday equation, high voltages can be induced in the electrical heating device as a result, which results in potential differences between the lightning conductor and the heating device or between the lightning conductor and the electrical conductors connected to the heating device. Depending on the current gradient and the geometric relationships in the rotor blade, these potential differences can amount to several megavolts, with the result that flashovers occur between the lightning conductor and the electrical heating device or the electrical conductors. This can result in damage to the heating device or adjacent structures of the rotor blade, up to total damage.
U.S. Pat. No. 7,729,100 discloses a wind turbine rotor blade having a supporting structure consisting of carbon fibers. The wind turbine rotor blade does not have an electrical heating device. A lightning conductor is connected to metal plates on the supporting structure via a plurality of cables in order to bring about equipotential bonding between the lightning conductor and the electrically conductive supporting structure.
Publication WO 2011/148049 A1 discloses a wind turbine rotor blade having a box-shaped supporting structure and profile leading edges and profile end edges attached thereto. An electrical heating device which has a plurality of heating wires is provided in the region of the profile leading edges. In addition, there is a plurality of lightning conductors, which are arranged distributed over the box-shaped supporting structure and the profile leading edges.
U.S. Pat. No. 6,612,810 discloses a wind turbine rotor blade having a central lightning conductor arranged approximately centrally in the rotor blade. A lightning receptor arranged in the region of the rotor blade tip is connected to this central lightning conductor. An electrical heating device having a plurality of electrical heating elements is provided in the region of the profile leading edge.
The electrical heating elements are connected to two electrical connecting lines running in the longitudinal direction of the rotor blade, with the result that a heating current can be supplied to the electrical heating elements. Those ends of the electrical connecting lines for the heating elements which are on the rotor blade tip side are connected to the lightning receptor via spark gaps. As a result, some of the lightning current is intended to be discharged by the electrical connecting lines of the heating elements, with the result that these connecting lines also act as lightning conductors. The potential difference between the two connecting lines should always be zero or so low that the heating elements cannot be damaged by the lightning strike.